This proposal is designed to provide circuit-dynamics understanding of anhedonia, a psychiatric symptom domain of enormous clinical significance that is well-suited for study in laboratory animals. In Aim 1, we generate high-resolution brainwide maps of endogenous and stimulus-triggered activity patterns in anhedonic states. We use our new readout technologies including ofMRI and COLM as described in the proposal, and our custom recombinase-driver rat lines to allow versatile mechanistic experiments determining if changes in dynamics are linked to altered activity in specific modulatory systems. In Aim 2, we employ another new technology (fiber photometry) to track and quantify local high-speed dynamical patterns corresponding to anhedonia, allowing observation during free behavior of relative balance and joint activity relationships across the brain (initially, we will test for evience of competition between prefrontal cortex and midbrain to exert influence over subcortical limbic pathways during behavior, following up our preliminary findings). In Aim 3, we test causal significance for anhedonia of the changes in dynamics identified in Aims 1 and 2, using new optogenetic tools to modulate coordinated activity relationships across the brain to induce anhedonia from baseline, and restore hedonic behavior in induced anhedonic states. We will also come full circle to Aim 1 measures, quantifying global activity patterns elicited by optical recruitment of the implicated circuit elements, in a final step toward identifying circuit-level phenotypes with causal explanatory power for anhedonic behavior. Together, the approaches proposed here will integrate novel technology to probe fundamental causal underpinnings and mechanisms of a key psychiatric symptom domain in freely-moving mammals.